The present invention relates to fire retardant foam materials. More particularly, the present invention relates to fire retardant polyurethane flexible foam materials and methods of producing the same, whereby fire retardant materials are deposited in the cell structure of the foam to inhibit propagation of flame throughout the foam mass.
Previous methods for producing fire retardant polyurethane flexible and semi-flexible foams have included incorporating into the formulation, prior to the foam reaction taking place, a variety of ingredients such as halogenated phosphorus compounds and, more recently, alumina trihydrate to obtain flame spread values as required by various tests. Thus, for example, automotive tests require only small amounts of additives and the foams exhibit a low degree of fire retardancy. While such treated foam may self-extinguish itself when exposed to a flame while in the horizontal position, the specimen may nevertheless burn readily if placed in a vertical position.
Some agencies have more stringent test parameters which require that the specimen be tested in the vertical position. To meet such parameters, higher loadings of fire retardants are necessary in the formulation, reducing some physical properties of the foam and significantly increasing foam density.
In some instances, foams utilized in the manufacture of furnishings for public places must pass a "Radiant Panel Test", also known as ASTME-162-79. This test requires the foam to be tested at a 45 degree angle while placed in a chamber at elevated temperature. In order to pass such a test, it has been necessary in one case to use a mixture of additives which increases the density of the foam from 1.3 lbs. per cubic foot to 4 lbs. per cubic foot.
An important consideration related to fire retardancy in urethanes is the migrating phenomenon of the additives. Also, there is evidence to indicate that some foams may lose their fire retardancy upon aging.
In U.S. Pat. Nos. 3,717,597 and 3,730,917 there are described various methods of obtaining a degree of fire retardancy. Both of these prior art patents are concerned with the use of regenerated scrap foam, i.e. scrap foam which is chopped into pieces and then glued together to form a usable piece. In U.S. Pat. No. 3,717,597, the method described therein employs urea to obtain a degree of fire retardancy.
The present invention deals with the use of virgin foam rather than foam of the rebonded type. The prior art patents are concerned with a composite (regenerated foam). Also, the prior art patents are concerned with mixing the urea with the foam particulate in a vat and adding adhesive. In the present invention, on the other hand, solid particulate material is deposited inside the cells of the foam, and such solid particulate material acts as a fire retardant.
By the present invention, there are provided fire retardant foam materials and methods of producing fire retardant polyurethane foams derived from polyethers and polyesters, with such foams having highly fire retardant properties which are imparted to the foam after it is produced. The present method includes depositing and encapsulating within the previously manufactured polyurethane foam cell structure, which may be either flexible or semi-flexible, certain materials or compounds which function as flameproofing or fire retardant agents, inhibiting propagation of the flame throughout the foam mass. The terms "flameproofing" and "fire retardant" are used interchangeably throughout the present specification and claims.
In one embodiment, the invention includes passing previously formed foam material in a compressed condition through a solution or dispersion of a fire retardant compound in a liquid medium, followed by allowing the foam material to dry, with the fire retardant material being retained within the cellular structure of the foam. Fire retardant compounds or materials which have been found to be useful in this embodiment of the invention include, ammonium sulfate, sodium bicarbonate and urea, with each of such materials being employed in the form of a solution or dispersion in water.
In variation of this embodiment, a small amount, less than 10% by weight, or a casein based glue or adhesive composition is added to stimulate adhesion of the solid particles within the foam cell structure.
An alternative embodiment of the invention is a dry process in which the foam material is subjected to one or more compressions in the presence of a dust atmosphere wherein the dust particles are of the desired fire retardant material. The foam material absorbs and retains the dust particles within the cell structure of the foam. Fire retardant compounds or materials which have been found to be useful in this embodiment include urea, ammonium, sulfate and sodium bicarbonate.